Geared turbofan arrangement with core split power ratio

ABSTRACT

A gas turbine engine according to an example of the present disclosure includes, among other things, a fan section, and a compressor section including at least a first compressor section and a second compressor section. A power ratio is provided by the combination of the first compressor section and the second compressor section. A method of design a gas turbine engine is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/177,372, filed on Feb. 11, 2014, which claims priority toU.S. Provisional Application No. 61/898,731, filed on Nov. 1, 2013; andU.S. Provisional Application No. 61/899,464, filed on Nov. 4, 2013.

BACKGROUND

This application relates to a core arrangement for a gas turbine engine.

Gas turbine engines are known, and typically include a fan deliveringair into a low pressure compressor section. The air is compressed in thelow pressure compressor section, and passed into a high pressurecompressor section. From the high pressure compressor section the air isintroduced into a combustion section where it is mixed with fuel andignited. Products of this combustion pass downstream over a highpressure turbine section, and then a low pressure turbine section.

Traditionally, the low pressure turbine section has driven both the lowpressure compressor section and a fan directly. As fuel consumptionimproves with larger fan diameters relative to core diameters it hasbeen the trend in the industry to increase fan diameters. However, asthe fan diameter is increased, high fan blade tip speeds may result in adecrease in efficiency due to compressibility effects. Accordingly, thefan speed, and thus the speed of the low pressure compressor section andlow pressure turbine section (both of which historically have beencoupled to the fan via the low pressure spool), has been a designconstraint.

More recently, gear reductions have been proposed between the lowpressure spool (low pressure compressor section and low pressure turbinesection) and the fan.

SUMMARY

A gas turbine engine according to an example of the present disclosureincludes a fan section, a compressor section, including at least a firstcompressor section and a second compressor section, a turbine sectionincluding at least one turbine to drive the second compressor section,and a fan drive turbine to drive at least a gear arrangement to drivethe fan section. The turbine section includes at least two turbinestages upstream of the fan drive turbine. A power ratio is provided bythe combination of the first compressor section and the secondcompressor section. The power ratio is provided by a first power inputto the first compressor section and a second power input to the secondcompressor section. The power ratio is equal to, or greater than, 1.0and less than, or equal to, 1.4.

In a further embodiment of any of the foregoing embodiments, the powerratio is less than 1.27.

In a further embodiment of any of the foregoing embodiments, the fandrive turbine includes six or fewer stages.

In a further embodiment of any of the foregoing embodiments, the fansection is configured to deliver a portion of air into the compressorsection, and a portion of air into a bypass duct, and wherein a bypassratio, which is defined as a volume of air passing to the bypass ductcompared to a volume of air passing into the compressor section, isequal to or greater than 10.

In a further embodiment of any of the foregoing embodiments, a gearratio of the gear arrangement is greater than 2.6.

In a further embodiment of any of the foregoing embodiments, an overallpressure ratio is provided by the combination of the first compressorsection, the second compressor section and a fan root pressure rise ofthe fan section. The overall pressure ratio is equal to or greater than36.

In a further embodiment of any of the foregoing embodiments, the fansection defines a fan pressure ratio less than 1.50. The first turbinesection is configured to rotate at least 2.6 times faster than the fansection, and an overall pressure ratio is provided by the combination ofthe first compressor section, the second compressor section and a fanroot pressure rise of the fan section. The overall pressure ratio isequal to or greater than 36.

In a further embodiment of any of the foregoing embodiments, the firstcompressor section includes 3 or more stages and the second compressorsection includes between 8 and 15 stages.

In a further embodiment of any of the foregoing embodiments, the fandrive turbine includes three 3 to six 6 stages.

In a further embodiment of any of the foregoing embodiments, the fandrive turbine defines a fan drive turbine pressure ratio that is greaterthan five.

A gas turbine engine according to an example of the present disclosureincludes a fan section, and a compressor section, including at least afirst compressor section and a second compressor section. The firstcompressor section includes 3 or more stages and the second compressorsection including 6 or more stages. A turbine section includes at leastone turbine to drive the second compressor section and a fan driveturbine to drive at least a gear arrangement to drive the fan section.The turbine section includes at least 2 turbine stages upstream of thefan drive turbine. A power ratio is provided by the combination of thefirst compressor section and the second compressor section, with thepower ratio being provided by a first power input to the firstcompressor section and a second power input to the second compressorsection. The power ratio is equal to or greater than 1.0. An overallpressure ratio is provided by the combination of the first compressorsection. The second compressor section and a fan root pressure rise ofthe fan section. The overall pressure ratio is equal to, or greaterthan, 36.

In a further embodiment of any of the foregoing embodiments, the fansection defines a fan pressure ratio less than 1.50, a gear ratio of thegear arrangement is greater than 2.6, the turbine section includes atleast 2 turbine stages upstream of the fan drive turbine, and the fandrive turbine includes 3 to 6 stages.

In a further embodiment of any of the foregoing embodiments, the powerratio is between 1.0 and 1.4.

In a further embodiment of any of the foregoing embodiments, the fansection defines a fan pressure ratio less than 1.45.

In a further embodiment of any of the foregoing embodiments, the fandrive turbine defines a fan drive turbine pressure ratio that is greaterthan five (5).

In a further embodiment of any of the foregoing embodiments, the powerratio is less than 1.27.

In a further embodiment of any of the foregoing embodiments, the fansection is configured to deliver a portion of air into the compressorsection, and a portion of air into a bypass duct, and wherein a bypassratio, which is defined as a volume of air passing to the bypass ductcompared to a volume of air passing into the compressor section, isequal to or greater than 12.

A gas turbine engine according to an example of the present disclosureincludes a fan section, a compressor section, including at least a firstcompressor section and a second compressor section, a turbine sectionincluding at least one turbine to drive the second compressor section,and a fan drive turbine to drive at least a gear arrangement to drivethe fan section. A power ratio is provided by the combination of thefirst compressor section and the second compressor section, with thepower ratio being provided by a first power input to the firstcompressor section and a second power input to the second compressorsection. The power ratio is equal to or less than 1.4. An overallpressure ratio is provided by the combination of the first compressorsection, the second compressor section and a fan root pressure rise ofthe fan section. The overall pressure ratio is equal to or greater than36.

In a further embodiment of any of the foregoing embodiments, the firstcompressor section includes 3 or more stages. The second compressorsection includes 6 or more stages. The turbine section includes at least2 turbine stages upstream of the fan drive turbine, and the fan driveturbine includes three 3 to six 6 stages.

In a further embodiment of any of the foregoing embodiments, the powerratio is greater than or equal to 1.0.

In a further embodiment of any of the foregoing embodiments, the fansection is configured to deliver a portion of air into the compressorsection, and a portion of air into a bypass duct, and wherein a bypassratio, which is defined as a volume of air passing to the bypass ductcompared to a volume of air passing into the compressor section, isequal to or greater than 10.

A method of designing a gas turbine engine according to an example ofthe present disclosure includes providing a fan section, providing acompressor section, including a first compressor section and a secondcompressor section, and providing a turbine section including at leastone turbine to drive the second compressor section and a fan driveturbine to drive the fan section via a gear arrangement. A power ratiois provided by the combination of the first compressor section and thesecond compressor section, with the power ratio being provided by afirst power input to the first compressor section and a second powerinput to the second compressor section. The power ratio is equal to orless than 1.4 at a predetermined design target. An overall pressureratio is provided by the combination of the first compressor section thesecond compressor section and a fan root pressure rise of the fansection. The overall pressure ratio is equal to or greater than 36 atthe predetermined design target.

In a further embodiment of any of the foregoing embodiments, thepredetermined design target is defined at sea level and at a static,full-rated takeoff power condition.

In a further embodiment of any of the foregoing embodiments, thepredetermined design target is defined at a cruise condition.

In a further embodiment of any of the foregoing embodiments, the firstcompressor section includes 3 or more stage. The second compressorsection includes 6 or more stages. The second compressor section ispositioned downstream of the first compressor section. The fan driveturbine includes three 3 to six 6 stages, and the at least one turbineincludes fewer stages than the fan drive turbine.

In a further embodiment of any of the foregoing embodiments, the powerratio is greater than or equal to 1.0.

These and other features of this disclosure will be better understoodupon reading the following specification and drawings, the following ofwhich is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a gas turbine engine.

FIG. 2 schematically shows the arrangement of the low and high spool,along with the fan drive of FIG. 1.

FIG. 3 schematically shows an alternative drive arrangement of FIG. 1.

FIG. 4 schematically shows a gas turbine engine including a three-spoolarchitecture.

FIG. 5 graphically shows the relationship of propulsive efficiency,thermal efficiency, and overall efficiency for a gas turbine engineembodiment.

FIG. 6 illustrates a perspective view of a turbine blade.

FIG. 6A illustrates a cross-sectional view of a portion of the turbineblade of FIG. 6 having a directionally solidified microstructure.

FIG. 7 illustrates a cross-sectional view of a portion of a fan case.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle 15, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. In some embodiments, thegear reduction ratio is less than about 5.0, or less than about 4.0. Forthe purposes of this disclosure, the term “about” means±3% unlessotherwise indicated. It should be understood, however, that the aboveparameters are only exemplary of one embodiment of a geared architectureengine and that the present invention is applicable to other gas turbineengines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7°R)]^(0.5). The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

FIGS. 2 and 3 schematically illustrate engines 220 and 320, each whichmay generally have the features of engine 20 in FIG. 1. As shown in FIG.2, the engine 220 may be counter-rotating. This means that the low speedspool 30, including the low pressure turbine 46 and low pressurecompressor 44, rotates in one direction (“−”), while the high speedspool 32, including high pressure turbine 54 and high pressurecompressor 52, rotates in an opposed direction (“+”). The gear reduction48, which may be, for example, an epicyclic transmission (e.g., with asun, ring, and star gears), is selected such that the fan 42 rotates inthe same direction (“+”) as the high spool 32. In FIG. 3, the fan 42 ofengine 320 rotates in the same direction as the low speed spool 30. Toachieve this rotation, the gear reduction 48 may be a planetary gearreduction which would cause the fan 42 to rotate in the same direction.Of course, this application extends to engines where the two spoolsrotate in the same direction.

FIG. 4 schematically illustrates an engine 420 arranged as a three-spoolarchitecture. The engine includes similar features as the engine 20 andalso has an intermediate spool 31. The intermediate spool 31 generallyincludes a low pressure compressor 44 and an intermediate pressureturbine 47 interconnected by a shaft extending along the engine centrallongitudinal axis A. The low speed spool 30 includes a low pressure orfan drive turbine 46 interconnected with a fan 42. In some embodiments,the engine 420 includes a gear reduction 48 positioned between the lowpressure turbine 46 and the fan 42. The gear reduction 48 can be locatedadjacent to the fan 42 (shown) or adjacent to the low pressure turbine46 as is known in the art. The fan 42 can be configured to rotate in thesame direction or in the opposite direction as the low pressure turbine46 via the gear reduction 48. In other embodiments, the gear reduction48 is omitted. With the arrangement of any of the engines 20, 220, 320,420, and with the other structure as set forth below, including thevarious quantities and operational ranges, the overall efficiency of thegas turbine engine is greatly increased.

Specific thrust can be used to evaluate the relative bulk of the engine.Specific thrust can be defined in one of two ways as:

SpecificThrust=(F _(Net))/(W _(Atotal))  Equation 1:

SpecificThrust=(1/g _(c))/(V _(Jet) −V _(o))  Equation 2:

where (F_(Net)) is the net thrust of the engine measured in (lbf),(W_(Atotal)) is the total inlet air mass flow of the engine measured in(lbm per second), (g_(c)) is the gravity constant (32.174 feet×lbm perlbf per second per second), (V_(Jet)) is the exhaust velocity measuredin (feet per second) at the exit of the engine exhaust nozzle, (V_(o))is the flight velocity of the aircraft, and specific thrust(SpecificThrust) is measured in lbf/(lb/s). If an aircraft includes morethan one engine exhaust nozzle, then (V_(Jet)) can be defined as theaverage of the exhaust velocities of the nozzles. Engines with a lowspecific thrust are relatively larger in size but have relatively betterjet noise and fuel consumption characteristics as compared to engineswith a high specific thrust.

The overall efficiency (“η_(overall)”) of a gas turbine engine can beevaluated in terms of its fuel economy or TSFC defined as follows:

TSFC=(V _(o)/η_(overall))×((3600 seconds/hr)/(J×LHV))  Equation 3:

where (J) is Joule's derived energy conversion (778 ft×lbf per Btu),(η_(overall)) is the overall efficiency of the engine, and (LHV) is thefuel lower heating value measured in (Btu divided by lbm). As shown,TSFC increases as flight velocity (V_(o)) of the aircraft increases, andimprovements in the overall efficiency of the engine (η_(overall))decrease TSFC. Thus, it is desirable to improve the overall efficiency(η_(overall)) of the engine.

In this disclosure, the overall efficiency of the engine (η_(overall))is defined as:

η_(overall)=(η_(propulsive)×η_(thermal))  Equation 4:

where (η_(propulsive)) is the propulsive efficiency of the engine, andwhere (η_(thermal)) is the thermal efficiency of the engine. In turn,thermal efficiency (η_(thermal)) and propulsive efficiency(η_(propulsive)) can be defined as:

η_(thermal)=(CorePower/FuelPower)  Equation 5:

η_(propulsive)=(ThrustPower/CorePower)  Equation 6:

where thrust power (ThrustPower) is the net thrust of the engine(F_(NET)) measured in (lbf multiplied by the flight velocity (V_(o))measured in ft. per second of the aircraft), fuel power (FuelPower) isthe fuel flow rate measured in (lbm/hr multiplied by the fuel lowerheating value (LHV) divided by 3600 seconds per hr), and core power(CorePower) is the total power provided by the combination of thespools.

More specifically, thermal efficiency (η_(thermal)) and propulsiveefficiency (η_(propulsive)) can be defined as:

η_(thermal)=(CorePower/J)/({dot over (m)} _(fuel) ×LHV/3600seconds/hr)  Equation 7:

η_(propulsive)=(V _(o))[(g _(c)/2)×(F _(Net) /W _(Atotal))+V_(o))]  Equation 8:

where ({dot over (m)}fuel) is the fuel flow rate to the combustor 56measured in lbm (pounds mass) per hour.

FIG. 5 graphically shows the relationship between propulsive efficiency(x-axis), thermal efficiency (y-axis), and the resultant overallefficiency (z-axis) in a gas turbine engine embodiment applying thetechniques described herein as compared to prior engines. Enginedesigners have used various techniques to improve the fuel efficiency.Some approaches to improving fuel efficiency have included increasingthe operating pressures and temperatures of the compressor section 24and high pressure turbine 54 upstream of the fan drive turbine 46,precipitating the need for advanced materials in the turbine andcompressor sections.

Vector 62 illustrates efficiency improvements typical of theseapproaches. Vector 62 has a slope of about 75 to 90 degrees, with animprovement in overall efficiency (η_(overall)) of about 10%, and about3% to 0% higher propulsive efficiency (η_(propulsive)), respectively.Accordingly, these approaches have generally resulted in improvements tothe thermal efficiency (η_(thermal)) but with marginal improvements topropulsive efficiency (η_(propulsive)) of the engine as a byproduct.Rather, vector 62 demonstrates that prior designers have not beenconcerned with selecting techniques that consider improvements inthermal efficiency (η_(thermal)) and propulsive efficiency(η_(propulsive)) simultaneously. Approaches to improving propulsiveefficiency (η_(propulsive)) have included increasing the bypass ratio(BPR) of the fan section 22, which increases the size and weight of theengine.

Similarly, these approaches to improving propulsive efficiency(η_(propulsive)) have resulted in marginal improvements to overallefficiency (η_(overall)). However, the overall efficiency (η_(overall))or thrust specific fuel consumption (TSFC) of the engine can be improvedby defining an engine architecture that affects propulsive efficiency(η_(propulsive)) and thermal efficiency (η_(thermal)) simultaneously,via core power (CorePower).

One embodiment of the engine disclosed herein is illustrated as vector64. As shown, vector 64 has a slope of about 30 to 60 degrees, whichresults in an improvement in the overall efficiency (η_(overall)) of theengine of about 20%, and about 14% to 8% higher propulsive efficiency(η_(propulsive)), respectively, than prior engines illustrated by vector62.

The core power (CorePower) of a gas turbine engine can be defined as:

CorePower=(2×P _(High))/(1+(P _(High) /P _(Low)))  Equation 9:

where (P_(High)) is the horsepower provided by the high speed spool 32in a two-spool architecture, or the power provided by the high spool 32and the intermediate spool 31 in a three-spool architecture; and where(P_(Low)) is the horsepower provided by the low spool 30.

A core split power ratio of the high spool (P_(High)) (and intermediatespool in a three-spool architecture) and the low spool (P_(Low)) can bedefined as:

(P _(High) /P _(Low))=[((2×HP _(HPC)×η_(propulsive))(F _(Net) ×V_(o)))−1]  Equation 10:

where (HP_(HPC)) is the horsepower at the (second) high pressurecompressor 52 (and intermediate spool in a three-spool architecture).The core split power ratio is greater than 1.0 except whenconcurrently: 1) the number of stages of the high pressure compressor 52is less than the number of stages of the low pressure compressor 44; and2) the number of stages of the high pressure compressor 52 is less thanthe sum of the number of stages of the high pressure turbine 54 and thenumber of stages of the low pressure turbine 46. As illustrated byequation 10, the overall efficiency (η_(overall)) of the engine can beimproved by transferring power output from the high spool 32 to the lowspool 30. However, prior engine designs have avoided this approachbecause it imposes undesirable thermal and mechanical stresses on thefan drive turbine 46 based on an increase in power output to drive thefan 42.

In one embodiment made according to the above design, the net thrust(F_(Net)) of the engine is 4,650 lbs, the flight velocity (V_(o)) is 779ft/sec, the propulsive efficiency (η_(propulsive)) is 0.71, and thepower of the high pressure compressor 52 (HP_(HPC)) is 10,500 hp. Thus,using Equation 10 above, the core power ratio is:

Ratio=(P _(High) /P _(Low))=[((2×HP _(HPC)×η_(propulsive))/(F _(Net) ×V_(o)))−1]=[((2×10500×550×0.71)/(4650×779))−1]=1.26

where 1 unit of horsepower is equivalent to 550 ft-lbf/sec. In anotherembodiment, the ratio was about 1.2. In a further embodiment, the ratiowas about 0.8. With ratios in the 0.5 to 1.4 range, and with apropulsive efficiency equal to or greater than about 0.65, a veryefficient overall gas turbine engine is achieved. More narrowly, ratiosequal to or greater than about 0.71 are more efficient. Ratios in the0.77 to 1.3 range are even more efficient. Even more narrowly, ratios inthe 0.9 to 1.1 range are more efficient. In a further embodiment, theratio was about 1.0, with the horsepower at the each of the low and highspools 30, 32 being approximately equivalent. As a result of theseratios, in particular, the compressor section and turbine section can bemade much smaller than in the prior art, both in diameter and axiallength. In addition, the efficiency of the overall engine is greatlyincreased.

The overall efficiency of the disclosed gas turbine engine is muchhigher than in the prior art. The exemplary gas turbine engine A(described above) and exemplary gas turbine engine B are compared to adirect-drive comparison engine C and a direct-drive base comparisonengine D, and can be found in Table 1 as follows:

TABLE 1 Comp. Base Engine Engine Engine Engine A B C D Net Thrust (FNet)(lbs) 4650 3925 4880 14158 Flight Velocity (Vo) (ft/sec) 779 779 779 828 Propulsive Efficiency 0.71 0.71 0.67     0.65 (η_(propulsive))Power, High Pressure 10500 8950 12730  39838* Compressor (HP_(HPC)) CoreSplit Power Ratio 1.26 1.29 1.48     1.44 (P_(High)/P_(Low)) RelativeImprovement 8.6% 9.0% 3.1% Base (0%) Propulsive Efficiency(η_(propulsive)) Thermal Efficiency 0.54 0.53 0.55     0.56 (thermal)Relative Improvement −2.7% −5.0% −2.1% Base Thermal Efficiency(η_(thermal)) (0%) Overall Efficiency (η_(overall)) 0.38 0.38 0.37    0.36 Relative Improvement 5.6% 3.6% 0.8% Base Overall Efficiency(η_(overall)) (0%) TSFC 0.51 0.52 0.53     0.57 Relative Improvement−10.9% −9.2% −6.7% Base TSFC (0%) *includes HP for a high pressurecompressor and an intermediate pressure compressorThus, as shown in Table 1, while comparison engine C has a core powerratio of 1.48, comparison engine C has a lower relative improvement inpropulsive efficiency (η_(propulsive)) and overall efficiency(η_(overall)) than the exemplary gas turbine engines A and B. Theexemplary gas turbine engines A and B also have more favorable relativeimprovements of TSFC than comparison engine C.

Similar benefits to the overall efficiency (η_(overall)) can be achievedby selecting an arrangement of the high pressure compressor 52 and lowcompressor 44 with respect to each other. The delta enthalpy risesacross the high pressure compressor 52 and the low pressure compressor44 can be expressed as:

(dh _(HPC))=T _(2.5) ×c _(p)×[(PR_(HPC)̂((γ−1)/(η_(polytropic)×γ)))−1]  Equation 11:

(dh _(LPC))=T _(2.0) ×c _(p)×[(PR_(LPC)̂((γ−1)/(η_(polytropic)×γ)))−1]  Equation 12:

where (T_(2.5)) is the temperature at the inlet of the high pressurecompressor 52 in a two-spool architecture (or approximately T_(2.2) in athree-spool arrangement, measured at the inlet to the intermediatepressure compressor 45), (PR_(HPC)) is the pressure ratio across thehigh pressure compressor 52 (and from the inlet of the intermediatepressure compressor 45 to the exit of the high pressure compressor 52 ina three-spool arrangement), (T_(2.0)) is the temperature at the inlet ofthe low pressure compressor 44 in a two-spool architecture (orapproximately T₁ in a three-spool arrangement, measured at the inlet tofan 42), (PR_(LPC)) is the pressure ratio across the low pressurecompressor 44 (or the pressure ratio across the fan 42 in a three-spoolarrangement), (γ) is the ratio of (c_(p)) to (c_(v)), with (c_(p)) beingthe specific heat capacity measured for a constant pressure process inBtu per lbm per degree Rankine (°R), and being (c_(v)) is the specificheat capacity measured for a constant volume process in Btu per lbm perdegree Rankine (°R). Temperatures (T_(2.0)), (T_(2.2)), and (T_(2.5))are measured in degree Rankine (°R).

The core split power ratio (P_(High)/P_(Low)) can be approximated by aratio of the delta enthalpy rises across the compressors as:

(P _(High) /P _(Low))=(dh _(HPC))/(dh _(LPC))  Equation 13:

where (dh_(HPC)) is the delta enthalpy rise across the high pressurecompressor 52 measured as exit minus inlet per lb. of airflow throughthe high pressure compressor 52, and where (dh_(LPC)) is the deltaenthalpy rise across the low pressure compressor 44 measured as exitminus inlet per lb. of airflow through the low pressure compressor 44.In some examples, engine 20 is designed to define a core split powerratio at a predetermined design target. In some examples, thepredetermined design target is defined at sea level and at a static,full-rated takeoff power condition. In other examples, the predetermineddesign target is defined at a cruise condition.

With ratios of the delta enthalpy rises similar to the core split powerratios disclosed herein, a very efficient overall gas turbine engine isachieved. In the illustrated embodiment, the low pressure compressor 44includes fewer stages than the high pressure compressor 52. In someembodiments, the low pressure compressor 44 includes 3 or more stages,or more narrowly 3 to 6 stages, such as 4 stages, and the high pressurecompressor 52 includes 6 or more stages, or 15 or fewer stages. In someembodiments, the high pressure compressor 52 includes 7 to 15 stages,such as 8 stages. In the illustrated embodiment, the high pressureturbine 54 includes fewer stages than the low pressure turbine 46. Infurther embodiments, the turbine section 28 includes at least 2 turbinestages upstream of the fan drive turbine 46. In embodiments, the fandrive turbine 46 includes 3 or more stages, or 6 or fewer stages. Insome embodiments, the fan drive turbine 46 includes between 3 and 6stages, such as 5 stages (shown in FIG. 1).

The core split power ratios disclosed herein can be combined with one ormore features to further improve the propulsive efficiency(η_(propulsive)) of the engine. As shown in FIG. 6, the turbine section28, more particularly the low pressure turbine 46, for example, caninclude one or more turbine blades 29 with features permitting higherinlet temperatures, higher rotational speeds and gear reduction ratiosthan conventional turbines. The turbine blade 29 includes an airfoil 33extending radially outward from a root 35. The blade 29 can include oneor more cooling features 37 configured to receive coolant from a coolantsource 43 (shown schematically) for cooling the blades 29, as is knownin the art. In some embodiments, the coolant source 43 is the compressorsection 24. The cooling features 37 can be one or more plenums and/orpassages formed in the turbine blade 29 to provide impingement orconvection cooling. In some embodiments, the cooling features 37 providecoolant to one or more cooling holes 39 for providing film cooling. Eachturbine blade 29 can be made of a directionally solidified material(shown schematically in FIG. 6A) or a single-crystal material.Directionally solidified materials include a microstructure having aplurality of elongated grains 66 that are parallel to the major stressaxes of the component as is known in the art. Each of the elongatedgrains 66 can extend the along the airfoil 33 between the root 35 andblade tip 51. Single crystal materials are formed as a single,homogenous crystal of material that includes no grain boundaries in thematerial, or rather, consist of only one grain. Single crystal materialscan include nickel-based super alloys such as Nickel aluminide (NiAl).In further embodiments, the turbine section 28 includes at least twoturbine stages upstream of the fan drive turbine 46. Modification of thelow pressure turbine 46 with these features enables redistribution ofhorsepower from the high spool 32 to the low spool 30, which can furtherresult in a reduction of the number of stage counts in the high pressurecompressor 52 and a more compact engine arrangement.

In another embodiment, the fan section 22 includes a hardwallcontainment system 70 (shown schematically in FIG. 1) arranged about theengine axis A and spaced radially from the fan blades 42. The hardwallcontainment system 70 is configured to contain, and absorb the impactof, a fan blade 42 separating from a fan hub 41 (shown schematically inFIG. 1) or a fragment thereof. In some embodiments, the hardwallcontainment system 70 is a hard ballistic liner applied to the nacelleor fan case 15 as is known in the art. The hard ballistic liner caninclude a rigid material such as a resin impregnated fiber structure,metallic structures, or ceramic structures. However, other materials andstructures of the hardwall containment system 70 are contemplated. Inyet another embodiment, the fan section 22 includes a fan case 15 madeof an organic matrix composite (shown schematically in FIG. 7). Theorganic matrix composite can include a matrix material 72 andreinforcement fibers 74 distributed through the matrix material 72. Thereinforcement fibers 74 may be discontinuous or continuous, dependingupon the desired properties of the organic matrix composite, forexample. The matrix material 72 may be a thermoset polymer or athermoplastic polymer. The reinforcement fibers 74 may include carbongraphite, silica glass, silicon carbide, or ceramic. Given thisdescription, one of ordinary skill in the art will recognize that othertypes of matrix materials and reinforcement fibers may be used. Infurther embodiments, the fan section 22 includes a fan blade and a diskwith a characteristic density of less than about 13.1 pounds per in̂2 offrontal area with respect to the engine. In some embodiments, the fansection 22 has a fan blade efficiency greater than about 94.5%, beingdefined as the amount of thrust generated by the fan blade 42 comparedto the work provided to the fan blade 42 by the gear reduction 48 or lowspeed spool 30. In further embodiments, the bypass ratio (BPR) which isdefined as a volume of air passing to the bypass duct compared to avolume of air passing into the compressor section 24 is greater thanabout 12:1. In some embodiments, the bypass ratio is less than aboutthirty (30), or more narrowly less than about twenty (20).

The core power ratios disclosed herein can be combined with one or morefeatures to further improve the thermal efficiency (η_(thermal)) of theengine, expressed below in quantities at a flight condition of 0.8 Machand 35,000 feet. In some embodiments, the low pressure turbine 46 isconfigured to rotate at least about 2.6 times faster than the fansection 22 and preferably at least about 2.9 times faster than the fansection 22. In further embodiments, an overall pressure ratio (OPR) ofthe engine provided by a combination of the low pressure compressor 44and the high pressure compressor 52 and the pressure rise at the root ofthe fan section 22 is equal to or greater than about 36. In anotherembodiment, the fan section 22 defines a fan pressure ratio less thanabout 1.50 and preferably less than about 1.40, the low pressure turbine46 is configured to rotate at least about 2.6 times faster than the fansection 22 and preferably at least 2.9 times faster than the fan section22, the overall pressure ratio is equal to or greater than about 36corresponding to a predetermined design target, and the turbine section28 includes at least two turbine stages upstream of the low pressureturbine 46. In other examples, an overall pressure ratio correspondingto the predetermined design target is greater than or equal to about40:1, or greater than or equal to about 50:1. In examples, the overallpressure ratio corresponding to the predetermined design target is lessthan or equal to about 80:1, or more narrowly less than or equal toabout 60:1.

In some embodiments, the fan section 22 has a fan blade efficiencygreater than about 94.5%, the fan drive turbine 46 has a thermalefficiency greater than about 90.9%, and the low pressure compressor 44has a thermal efficiency of at least about 87% and is configured todeliver air to the high pressure compressor 52 having a thermalefficiency of at least about 85.1%. With respect to the compressorsection 24, thermal efficiency can be defined as the pressure riseversus the temperature rise between an inlet and an outlet of one of thelow pressure and high pressure compressors 44, 52. Thermal efficiencywith respect to the fan drive turbine 46 is defined as the pressuredecrease between the inlet and the outlet as compared to the worktransferred to the low speed spool 30. In further embodiments, thecooling air flow to the turbine section 28 is less than or equal toabout 36% of the core airflow along the core airflow path C, whichincreases the amount of compressed air provided to the combustor section26. In other embodiments, the gear arrangement 48 has a thermalefficiency at sea-level takeoff and at stationary conditions of greaterthan about 98.7% as measured by the oil temperature rise between aninlet and an outlet of the gear arrangement 48.

Engines made with the disclosed architecture, and including spoolarrangements as set forth in this application, and with modificationscoming from the scope of the claims in this application, thus providevery high efficient operation, have increased fuel efficiency, and arecompact and lightweight relative to their thrust capability. Two-spooland three-spool direct drive engine architectures can also benefit fromthe teachings herein.

It should be understood that relative positional terms such as“forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like arewith reference to the normal operational attitude of the vehicle andshould not be considered otherwise limiting.

While this invention has been disclosed with reference to oneembodiment, it should be understood that certain modifications wouldcome within the scope of this invention. For that reason, the followingclaims should be studied to determine the true scope and content of thisinvention.

What is claimed is:
 1. A gas turbine engine comprising: a fan section; acompressor section, including at least a first compressor section and asecond compressor section; a turbine section including at least oneturbine to drive said second compressor section and a fan drive turbineto drive at least a gear arrangement to drive said fan section, saidturbine section including at least two turbine stages upstream of saidfan drive turbine; and wherein a power ratio is provided by thecombination of said first compressor section and said second compressorsection, with said power ratio being provided by a first power input tosaid first compressor section and a second power input to said secondcompressor section, said power ratio being equal to, or greater than,1.0 and less than, or equal to, 1.4.
 2. The gas turbine engine as setforth in claim 1, wherein said power ratio is less than 1.27.
 3. The gasturbine engine as set forth in claim 1, wherein said fan drive turbineincludes six or fewer stages.
 4. The gas turbine engine as set forth inclaim 3, wherein said fan section is configured to deliver a portion ofair into said compressor section, and a portion of air into a bypassduct, and wherein a bypass ratio, which is defined as a volume of airpassing to said bypass duct compared to a volume of air passing intosaid compressor section, is equal to or greater than
 10. 5. The gasturbine engine as set forth in claim 3, wherein a gear ratio of saidgear arrangement is greater than 2.6.
 6. The gas turbine engine as setforth in claim 3, wherein an overall pressure ratio being provided bythe combination of said first compressor section, said second compressorsection and a fan root pressure rise of said fan section, said overallpressure ratio being equal to or greater than
 36. 7. The gas turbineengine as set forth in claim 1, wherein said fan section defines a fanpressure ratio less than 1.50, said first turbine section is configuredto rotate at least 2.6 times faster than said fan section, and anoverall pressure ratio being provided by the combination of said firstcompressor section, said second compressor section and a fan rootpressure rise of said fan section, said overall pressure ratio beingequal to or greater than
 36. 8. The gas turbine engine as set forth inclaim 1, wherein said first compressor section includes 3 or more stagesand said second compressor section includes between 8 and 15 stages. 9.The gas turbine engine as recited in claim 8, wherein said fan driveturbine includes three 3 to six 6 stages.
 10. The gas turbine engine asrecited in claim 9, wherein said fan drive turbine defines a fan driveturbine pressure ratio that is greater than five.
 11. A gas turbineengine comprising: a fan section; a compressor section, including atleast a first compressor section and a second compressor section, saidfirst compressor section including 3 or more stages and said secondcompressor section including 6 or more stages; a turbine sectionincluding at least one turbine to drive said second compressor sectionand a fan drive turbine to drive at least a gear arrangement to drivesaid fan section, said turbine section including at least 2 turbinestages upstream of said fan drive turbine; and wherein a power ratio isprovided by the combination of said first compressor section and saidsecond compressor section, with said power ratio being provided by afirst power input to said first compressor section and a second powerinput to said second compressor section, said power ratio being equal toor greater than 1.0; and wherein an overall pressure ratio is providedby the combination of said first compressor section, said secondcompressor section and a fan root pressure rise of said fan section,said overall pressure ratio being equal to, or greater than,
 36. 12. Thegas turbine engine as set forth in claim 11, wherein said fan sectiondefines a fan pressure ratio less than 1.50, a gear ratio of said geararrangement is greater than 2.6, said turbine section includes at least2 turbine stages upstream of said fan drive turbine, and said fan driveturbine includes 3 to 6 stages.
 13. The gas turbine engine as set forthin claim 11, wherein said power ratio is between 1.0 and 1.4.
 14. Thegas turbine engine as set forth in claim 11, wherein said fan sectiondefines a fan pressure ratio less than 1.45.
 15. The gas turbine engineas recited in claim 14, wherein said fan drive turbine defines a fandrive turbine pressure ratio that is greater than five (5).
 16. The gasturbine engine as set forth in claim 15, wherein said power ratio isless than 1.27.
 17. The gas turbine engine as recited in claim 16,wherein said fan section is configured to deliver a portion of air intosaid compressor section, and a portion of air into a bypass duct, andwherein a bypass ratio, which is defined as a volume of air passing tosaid bypass duct compared to a volume of air passing into saidcompressor section, is equal to or greater than
 12. 18. A gas turbineengine comprising: a fan section; a compressor section, including atleast a first compressor section and a second compressor section; aturbine section including at least one turbine to drive said secondcompressor section and a fan drive turbine to drive at least a geararrangement to drive said fan section; wherein a power ratio is providedby the combination of said first compressor section and said secondcompressor section, with said power ratio being provided by a firstpower input to said first compressor section and a second power input tosaid second compressor section, said power ratio being equal to or lessthan 1.4; and wherein an overall pressure ratio is provided by thecombination of said first compressor section, said second compressorsection and a fan root pressure rise of said fan section, said overallpressure ratio being equal to or greater than
 36. 19. The gas turbineengine as set forth in claim 18, wherein said first compressor sectionincludes 3 or more stages, said second compressor section includes 6 ormore stages, said turbine section includes at least 2 turbine stagesupstream of said fan drive turbine, and said fan drive turbine includesthree 3 to six 6 stages.
 20. The gas turbine engine as set forth inclaim 18, wherein said power ratio is greater than or equal to 1.0. 21.The gas turbine engine as set forth in claim 18, wherein said fansection is configured to deliver a portion of air into said compressorsection, and a portion of air into a bypass duct, and wherein a bypassratio, which is defined as a volume of air passing to said bypass ductcompared to a volume of air passing into said compressor section, isequal to or greater than
 10. 22. A method of designing a gas turbineengine comprising: providing a fan section; providing a compressorsection, including a first compressor section and a second compressorsection; providing a turbine section including at least one turbine todrive said second compressor section and a fan drive turbine to drivesaid fan section via a gear arrangement; wherein a power ratio isprovided by the combination of said first compressor section and saidsecond compressor section, with said power ratio being provided by afirst power input to said first compressor section and a second powerinput to said second compressor section, said power ratio is equal to orless than 1.4 at a predetermined design target; and wherein an overallpressure ratio is provided by the combination of said first compressorsection, said second compressor section and a fan root pressure rise ofsaid fan section, said overall pressure ratio being equal to or greaterthan 36 at the predetermined design target.
 23. The method as set forthin claim 22, wherein said predetermined design target is defined at sealevel and at a static, full-rated takeoff power condition.
 24. Themethod as set forth in claim 22, wherein said predetermined designtarget is defined at a cruise condition.
 25. The method as set forth inclaim 22, wherein said first compressor section includes 3 or morestages, said second compressor section includes 6 or more stages, saidsecond compressor section is positioned downstream of said firstcompressor section, said fan drive turbine includes three 3 to six 6stages, and said at least one turbine includes fewer stages than saidfan drive turbine.
 26. The method as set forth in claim 22, wherein saidpower ratio is greater than or equal to 1.0.